One of the conventionally known apparatus for detecting a lane marker on a driving road is a driving lane detector for vehicle arranged to take an image of a state of a driving road with a video camera set in the front part of the vehicle and to detect a type of a white line on the driving road on the basis of the image, as described in Japanese Patent Application Laid-Open No. 2000-14595. This is a device that detects candidate points for a white line by image processing of the image and that determines whether the white line is a solid line or a dashed line, based on the white line candidate point data and past detection rate data of white line candidate points.